The problem is all they're saying is it's capable of powering headphones that are rated at 600ohm, it doesn't really tell us much about it. As well from a quick search I can't find info on their site about any specs that really matter in this case. Many motherboards onboard solutions use this as a spec or marketing point. The issue is, some of your really really high end headphones(HD800's I hear) can be quite picky about amplifiers(or so I've heard). I can't imagine the K7XX's are super picky, but that doesn't mean they couldn't improve. It's also very possible they don't improve at all, or the improvement is incredibly minimal.
All that said, being that Creative tends to milk the "Gaming" teat(or has in the past), if any of their special gaming(or even non gaming) settings are turned on it could effect any perceived change in audio quality. I know sounds in CoD4 back in the day changed significantly when I got a Fatal1ty X-Fi card(likely the special gaming settings). I know most of this is speculation thanks to the issue of unknown specs that are usually used in the dac/amp world, but unless Creative did that bad of a job I'd expect the biggest possible change in sound to be from loss of any special "features."(if they're turned on)